This application is based upon and claims the benefit of priority of Japanese Patent Applications No. H.11-96487 filed on Apr. 2, 1999, No. H.11-195503 filed on Jul. 9, 1999 and No.2000-35674 filed on Feb. 8, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of effectively and reliably peeling off a necessary portion of a coating around a circumference of a conductor of an insulated conductive wire.
2. Description of Related Art
According to a conventional method of peeling off a coating of an insulated conductive wire having an elliptical cross section, as shown in FIGS. 20A and 20B, the insulated conductive wire 1 passes through a gap between a pair of grinding stones 5 urged respectively by biasing means such as springs in a direction of bringing the grinding stones 5 close to each other in such a manner that a distance between center axes of the pair of the grinding stones 5 may be varied by a force against the biasing means. That is, when the insulated conductive wire 1 is inserted between the pair of the grinding stones 5, the grinding stones 5 are pushed by the insulated conductive wire 1 so as to move in a direction of enlarging the distance between center axes of the pair of the grinding stones 5. The coating of the insulated conductive wire 1 may be peeled off by a relative movement of the insulated conductive wire 1 to the grinding stones 5 perpendicular to a longitudinal direction of the insulated conductive wire 1. A first grinding processing is carried out, as shown in FIG. 20A, in parallel with a longer diameter direction of the elliptical cross section of the insulated conductive wire 1. Then, a second grinding processing is carried out, as shown in FIG. 20B, perpendicularly to the longer diameter direction of the elliptical cross section of the insulated conductive wire 1 at a position where the grinding stones 5 are rotated relatively to the insulated conductive wire 1 by an angle of 90xc2x0 around a longitudinal axis thereof. With the conventional method mentioned above, it is intended to peel off the coating 11 all around an outer circumference of the insulated conductive wire 1.
However, mere grinding perpendicularly to both of the longer and shorter diameter directions of the cross section of the insulated conductive wire is likely to leave the coatings on four corner surfaces thereof. Further, though the method is effective and has no problem in a case that a connection of the coating to the conductor is relatively weak, in a case that the insulating resin coating is firmly connected to the conductor and the conductor is made of relatively soft metal such as copper, the method is likely to cause such problems that the coating is partly left on a surface of the conductor after the coating peeling process, a surface roughness control of the conductor is relatively troublesome, or the grinding is made so deeply into the conductor that the conductor becomes too thin.
The present invention has been made in view of the above mentioned problems, and an object of the present invention is to provide a method of peeling off the coating of the insulated conductive wire by cutting tools without leaving any part of the coating covering the conductor, with an easy control of surface roughness of the conductor and without cutting too deep into the conductor, even if the connection of the coating with the conductor is strong.
To achieve the above object, the method comprises steps of forming a groove nearly perpendicular to a longitudinal direction of the insulated conductive wire by removing the coating and a part of the conductor at a given position within a peeling region of the insulated conductive wire where the coating is to be peeled off, and, then, executing a first peeling process of peeling off the coating at the peeling region by making a first cutting edge cut deep into the conductor so as to penetrate through the coating at a position away from the groove and moving the first cutting edge relatively to the insulated conductive wire in a longitudinal direction thereof toward the groove.
With the method mentioned above, the coating may be completely peeled off since the cutting edge cuts relatively deep into the insulated conductive wire and chips or bars by cutting may be easily separated from a surface of the insulated conductive wire because of the groove perpendicular to a moving direction of the cutting edge.
It is preferable to have, in addition to (before or after) the first peeling process of peeling off the coating with the first cutting edge in the longitudinal direction of the insulated conductive wire, a second peeling process of peeling off the coating of a side surface of the insulated conductive wire by moving a second cutting edge relatively to the insulated conductive wire in a direction perpendicular to the longitudinal direction thereof. As a result, the coating all around the outer circumference of the insulated conductive wire at the peeling region may be completely peeled off.
Preferably, a width length of the second cutting edge corresponds to a length of the peeling region in a longitudinal direction of the insulated conductive wire. This makes it possible to peel off the coating along the peeling region in a longitudinal direction of the insulated conductive wire at one time cutting operation of the second cutting edge.
Further, it is preferable from effective and precise cutting processing standpoints that the coating of opposite side surfaces of the insulated conductive wire is simultaneously peeled off by a pair of the second cutting edges.
In place of the second peeling process mentioned above, the first peeling process by the first cutting edge may be repeated over entire surfaces at the peeling region of the insulated conductive wire. It is more effective to make two of the first cutting edges move toward the groove formed near in a longitudinal center of the peeling region from the opposite ends thereof. Preferably, the groove is formed all around a circumference of the insulated conductive wire for easily removing cutting chips from the conductor. A trapezoidal shape of the groove is preferable for easy removal of the cutting chips. The groove may be also used for easily dividing the insulated conductive wire into a piece after peeling off all coatings at the peeling region.
In case of the insulated conductive wire having a near square cross section, the coating may be peeled off by moving cutting tools relatively to the insulated conductive wire in parallel with the respective flat faces and perpendicularly to a longitudinal direction of the insulated conductive wire, while making the respective cutting tools cut deep into the conductor through the coating. It is preferable to use a pair of cutting edges for peeling off the coating on any two flat surfaces in opposite angle directions thereof.
To completely peel off the coating all around the circumference of the conductor, preferably, the coating on any one of corners between the adjacent two flat surfaces of the insulated conductive wire may be peeled off by moving the cutting tools perpendicularly to the longitudinal direction of the insulated conductive wire. This results in making the cross section of the insulated conductive wire form in an octagonal shape.
It is an another aspect of the present invention to provide a method of peeling off the coating by grinding. The coatings at the peeling region on any one corner surface of the four corner surfaces and on adjacent any two side surfaces of the four side surfaces is simultaneously peeled off by making the corner surface and the adjacent any two side surfaces come in contact with a grinding stone whose grinding surface has a profile corresponding to shapes of the any one corner surface and the adjacent two any side surfaces and moving the insulated conductive wire relatively to the grinding stone in a longitudinal direction thereof. According to this grinding method, the coating on the round corner surface may be completely peeled off.
By adjusting a rotating speed of the grinding stone and a roughness of the grinding surface thereof, the conductor at the peeling region may have a plurality of linear scratches extending in a longitudinal direction of the insulated conductive wire or a satin finished surface having a plurality of fine concave and convex portions after the coating peeling process. With the satin finished surface at the peeling region, two of the insulated conductive wires may be easily bonded to each other and the linear scratches serve to make the insulating resin flow smoothly. The insulating resin is generally used for protecting the insulated conductive wires after bonding thereof.